The System Life Cycle
Week
14
LBSC
690
Information
Technology
![](3D"slide0001_image001.jpg")
Agenda
&#=
8226;Questions
&#=
8226;Systems
analysis
&#=
8226;Building
complex systems
&#=
8226;Managing
complex systems
&#=
8226;Final
exam review
The System Life Cycle
&#=
8226;Systems
analysis
&=
#8211;How
do we know what kind of system to build?
&#=
8226;User-centered
design
&=
#8211;How
do we discern and satisfy user needs?
&#=
8226;Implementation
&=
#8211;How
do we build it?
&#=
8226;Management
&=
#8211;How
do we use it?
Systems Analysis
&#=
8226;First
steps:
&=
#8211;Understand
the task
&=
#8226;Limitations
of existing approaches
&=
#8211;Understand
the environment
&=
#8226;Structure
of the industry, feasibility study
&#=
8226;Then
identify the information flows
&#=
8211;e.g.,
Serials use impacts cancellation policy
&#=
8226;Only
then can you design a solution
Analyze the Information Flows
&#=
8226;Where
does information originate?
&=
#8211;Might
come from multiple sources
&=
#8211;Feedback
loops may have no identifiable source
&#=
8226;Which
parts should be automated?
&=
#8211;Some
things are easier to do without computers
&#=
8226;Which
automated parts should be integrated?
&#=
8226;What
other systems are involved?
&=
#8211;And
what information do they contain?
Analyzing Information Flows
•Process Modeling
–Structured anal=
ysis
and design
–Entity-relation=
ship
diagrams
–Data-flow
diagrams
–<=
/span>
•Object
Modeling
–Object-oriented
analysis and design
–Unified Modeling
Language (UML)
Some Library Activities
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&#=
8226;Acquisition
&#=
8226;Cataloging
&#=
8226;Reference
&=
#8211;Online
Public Access Catalog (OPAC)
&#=
8226;Circulation
&#=
8226;Weeding
&#=
8226;Reserve,
recall, fines, interlibrary loan, …
=
226;Budget,
facilities schedules, payroll, ...
Discussion Point:
Integrated Library System
Integrated Library System
<=
span
class=3DBB style=3D'position:absolute;left:-4.68%'>•What
functions should be integrated?
<=
span
class=3DBB style=3D'position:absolute;left:-4.64%'>•Which
of those should be automated?
User-Centered Design
&#=
8226;Start
with user needs
&=
#8211;Who
are the present and future users?
&=
#8211;How
can you understand their needs?
&#=
8226;Evaluate
available technology
&=
#8211;Off-the-shelf
solutions
&=
#8211;Custom-developed
applications
&#=
8226;Implement
something
&#=
8226;Evaluate
it with real users
The Waterfall Model
&#=
8226;Key
insight: invest in the design
stage
&=
#8211;An
hour of design can save a week of debugging!
&#=
8226;The
motivation behind DoD Standard 2167
&=
#8211;Requirements
&=
#8226;Specifies
what the software is supposed to do
&=
#8211;Specification
&=
#8226;Specifies
the design of the software
&=
#8211;Test
plan
&=
#8226;Specifies
how you will know that it did it
The Waterfall Model
![](3D"slide0040_image003.jpg")
![](3D"slide0040_image004.gif")
Requirements
Specification
Software
Test Plan
The Spiral Model
&#=
8226;Build
what you think you need
&=
#8211;Perhaps
using the waterfall model
&#=
8226;Get
a few users to help you debug it
&=
#8211;First
an “alpha” release, then a “beta” release
&#=
8226;Release
it as a product (version 1.0)
&=
#8211;Make
small changes as needed (1.1, 1.2, ….)
&#=
8226;Save
big changes for a major new release
&=
#8211;Often
based on a total redesign (2.0, 3.0, …)
![](3D"slide0042_image005.gif")
The Spiral Model
1.0
0.5
2.0
3.0
1.1
1.2
2.1
2.2
2.3
![](3D"slide0042_image006.gif")
![](3D"slide0042_image007.gif")
Some Unpleasant Realities<=
/div>
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&#=
8226;The
waterfall model doesn’t work well
&=
#8211;Requirements
usually incomplete or incorrect
&#=
8226;The
spiral model is expensive
&#=
8211;Redesign
leads to recoding and retesting
The Rapid Prototyping Model
&#=
8226;Goal:
explore
requirements
&=
#8211;Without
building the complete product
&#=
8226;Start
with part of the functionality
=
&=
#8211;That
will (hopefully) yield significant insight
&#=
8226;Build
a prototype
&=
#8211;Focus
on core functionality, not in efficiency
&#=
8226;Use
the prototype to refine the requirements
=
226;Repeat
the process, expanding functionality
![](3D"slide0045_image008.gif")
Rapid Prototyping + Waterfall
Update
Requirements
Choose
Functionality
Build
Prototype
Initial
Requirements
![](3D"slide0045_image009.gif")
![](3D"slide0045_image010.gif")
![](3D"slide0045_image011.gif")
![](3D"slide0045_image012.gif")
![](3D"slide0045_image013.gif")
Write
Specification
![](3D"slide0045_image014.gif")
Create
Software
![](3D"slide0045_image015.gif")
Write
Test Plan
![](3D"slide0045_image016.gif")
![](3D"slide0045_image017.gif")
![](3D"slide0045_image018.gif")
![](3D"slide0045_image019.gif")
![](3D"slide0045_image020.gif")
Implementation Requirements
&#=
8226;Availability
&=
#8211;Mean
Time Between Failures (MTBF)
&=
#8211;Mean
Time To Repair (MTTR)
&#=
8226;Capacity
&=
#8211;Number
of users for each application
&=
#8211;Response
time
&#=
8226;Flexibility
&=
#8211;Upgrade
path
Alternative Architectures<=
/div>
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&#=
8226;Batch
processing (e.g., recall notices)
&=
#8211;Save
it up and do it all at once
&#=
8226;Timesharing
(e.g., OPAC)
&=
#8211;Everyone
uses the same machine
&#=
8226;Client-Server
(e.g., Web)
&=
#8211;Some
functions done centrally, others locally
&#=
8226;Peer-to-Peer
(e.g., Kazaa)
&=
#8211;All
data and computation is distributed
Management Issues
&#=
8226;Retrospective
conversion
&=
#8211;Even
converting electronic information is expensive
&#=
8226;Management
information
&=
#8211;Peak
capacity evaluation, audit trails, etc.
&=
#8211;Sometimes
costs more to collect than it is worth!
&#=
8226;Training
&=
#8211;Staff,
end-users
&#=
8226;Privacy
Hands On: What Goes Wrong?=
&#=
8226;Check
out Risks Digest for a random date
&#=
8211;http://groups.google.com/groups?q=3Dcomp.risks
&=
#8211;Pick
a random date near your birthday
&#=
8226;Find
a case of unexpected consequences
&#=
8226;Try
to articulate the root
cause
&=
#8211;Not
the direct cause
Discussion Points:
Managing Complex Systems
Managing Complex Systems
&#=
8226;Critical
system availability
&=
#8211;Why
can’t we live without these systems?
&#=
8226;Understandability
&=
#8211;Why
can’t we predict what systems will do?
&#=
8226;Nature
of bugs
&=
#8211;Why
can’t we get rid of them?
&#=
8226;Auditability
&=
#8211;How
can we learn to do better in the future?
Critical Infrastructure Protectio=
n
<=
span
class=3DHBB style=3D'position:absolute;left:-9.66%'>•Banking
and finance
<=
span
class=3DHBB style=3D'position:absolute;left:-10.36%'>•Energy
<=
span
class=3DHBB style=3D'position:absolute;left:-10.36%'>•Transportation
<=
span
class=3DHBB style=3D'position:absolute;left:-9.95%'>•Emergency
services
<=
span
class=3DHBB style=3D'position:absolute;left:-9.56%'>•Food
and agriculture
SCADA: Supervisory Control and Data Acquisition
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National Cyberspace Strategy
&#=
8226;Response
system
&=
#8211;Analysis,
warning, response, recovery
&#=
8226;Threat
and vulnerability reduction
&#=
8226;Awareness
and training program
&=
#8211;Return
on investment, best practices
&#=
8226;Securing
government systems
&#=
8226;International
cooperation
Summary
&#=
8226;Systems
analysis
&=
#8211;Required
for complex multi-person tasks
&#=
8226;User-centered
design
&=
#8211;Multiple
stakeholders complicate the process
&#=
8226;Implementation
&=
#8211;Architecture,
open standards, …
&#=
8226;Management
&=
#8211;Typically
the biggest cost driver
Talk to Me About the Exam!=
&#=
8226;About
5 questions
&=
#8211;Same
question styles as the midterm
&=
#8211;Some
may require use of the computer
&#=
8226;Comprehensive
- covers the entire course
&=
#8211;Emphasis
and structure from the second half
&#=
8226;Two
hours
&#=
8226;Post-exam
discussion at Bentley’s
The Grand Plan
![](3D"slide0016_image021.gif")
Networks
XML
Multimedia
Computers
Databases
Programming
![](3D"slide0016_image022.gif")
Search
Interaction
Communication
Web
Life Cycle
Policy
![](3D"slide0016_image023.gif")
Integration
Midterm
![](3D"slide0016_image024.gif")
Project
Final
Computer Systems
&#=
8226;Hardware
&=
#8211;Types
of hardware
&=
#8211;Storage
hierarchy
&=
#8211;Moore’s
law
&#=
8226;Software
&=
#8211;Types
of software
&=
#8211;Types
of interfaces
![](3D"slide0018_image026.gif")
Networks
&#=
8226;Types
of Networks
&=
#8211;LAN,
WAN, Internet, Wireless
&#=
8226;Packet
Switching
&=
#8211;Ethernet,
routers, routing tables
&#=
8226;Layered
Architecture and protocols
&=
#8211;TCP/UDP
&=
#8211;IP
address/domain name
&#=
8226;Encryption
![](3D"slide0019_image028.gif")
Structured Documents
![](3D"slide0020_image030.gif")
![](3D"slide0020_image031.gif")
My Browser
•The Web
–HTTP, HTML,
URL
–<=
/span>
•XML
–DTD, XSL, XLink=
Multimedia
![](3D"slide0021_image033.jpg")
![](3D"slide0021_image034.gif")
&#=
8226;Compression,
compression, compression
&#=
8211;Images:
Lossy vs loseless
&#=
8211;Video: Frames are alike
&#=
8211;Speech:
Predictable characteristics
&#=
8211;Music: Masking
<=
/div>
&#=
8226;Streaming
![](3D"slide0021_image035.gif")
![](3D"slide0021_image036.gif")
Internet
Buffer
![](3D"slide0021_image038.gif")
Programming
•Balancing machines =
and
human needs
–Machines require
low-level specific instructions
–Humans require
high-level abstraction
•Object models repre=
sent
aspects of reality
•Can create any beha=
vior
from 3 control structures
–Sequential
execution
–Conditional
–Iteration
•Javascript interpre=
ters
are in Web browsers
![](3D"slide0022_image040.gif")
![](3D"slide0023_image042.gif")
Databases
&=
#8226;Structured
information
&=
#8211;Field->record->table->database
&=
#8211;Primary
key
&=
#8226;Normalized
tables (relations)
&=
#8211;Remove
redundancy, inconsistency, error
&=
#8226;“Join” links
tables
&=
#8211;Foreign
key
&=
#8226;Visual
programming in Access
Integration
&#=
8226;Multimedia
&=
#8211;SMIL
&#=
8226;Web-accessible
databases
&=
#8211;Cold
Fusion
The Web
![](3D"slide0025_image044.jpg")
Search
•Exact match
=
;
–<=
/span>
•Term-based rank=
ed
retrieval
–<=
/span>
•Recommender sys=
tems
–<=
/span>
•Web search
=
–Links and anchor
text
–<=
/span>
•Evaluation
Human-Computer Interaction=
&=
#8226;Human-machine
synergy
&=
#8226;Mental
models
&=
#8226;Input
and output devices
&=
#8226;Interface
types
=
–Direct
manipulation, menu, language based
![](3D"slide0027_image046.jpg")
Computer-Mediated Communication
&#=
8226;Synchronous
/ Asynchronous
&#=
8226;Remote
/ local
&#=
8226;One-to-one
/ many-to-many
&#=
8226;Computer-Supported
Cooperative Work
&#=
8226;Computers
as educational media
Policy
&=
#8226;Ownership
&=
#8211;Equitable
access
&=
#8211;Controlled
access
&=
#8226;Identity
&=
#8211;Choosing
good passwords
&=
#8226;Privacy
&=
#8211;Government
/ commercial
&=
#8226;Integrity
![](3D"slide0029_image048.gif")
Life Cycle
R.J. Bentley’s Filling Stat=
ion
![](3D"slide0034_image050.jpg")
Monday Dec 15, 2003 at 8:00 P.M.
Click to edit Master text styles
Second level
Third level
Fourth level
Fifth level
1
2
3
4
7
6
8
Barry Boehm 1988
9
10
13
14
A server
that sits between a client application,
such as a Web browser, and a real
server. It intercepts all requests to the real server to see if it can ful=
fill
the requests itself. If not, it forwards the request to the
real server. Proxy servers have two main purposes:
Improve
Performance: Proxy servers can dramatically improve performance for
groups of users. This is because it saves the results of all requests for =
a certain
amount of time. Consider the case where both user
X and user Y access the World Wide Web<=
/span>
through a proxy server. First user X requests a certain Web
page, which we'll call Page 1. Sometime later, user Y reque=
sts
the same page. Instead of forwarding the request to the Web serv=
er
where Page 1 resides, which can be a time-consuming operation, the p=
roxy
server simply returns the Page 1 that it already fetched for user X.
Since the proxy server is often on the same network
as the user, this is a much faster operation. Real proxy
servers support hundreds or thousands of users. The major online services
such as Compuserve and America Online<=
/span>,
for example, employ an array of proxy servers.
Filter
Requests: Proxy servers can also be used to filter requests. For=
example,
a company might use a proxy server to prevent its employees from accessing
a specific set of Web sites.
http://www.ece.purdue.edu/~ace/jp=
eg-tut/jpgimag1.html
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